This invention relates to a flat display panel, and more particularly to a sealing structure for a flat display panel such as a fluorescent display panel or a gas discharge tube which is hermetically sealed without a chip tube for exhausting air.
In the prior art, a flat display panel was provided with a chip tube projected therefrom for air exhaustion, but in recent years there have been demands for chip-less display panels.
Japanese Patent Application laid-open No. Sho 60-202637 laid open on Oct. 14, 1985 discloses a fluorescent display panel having a chip-less structure. In the disclosure initially, a through-hole is opened in the glass plate of an envelope. Then, after the inner electrodes are fabricated, the envelope is placed in a vacuum chamber and the through-hole is hermetically sealed in vacuum with a cover plate comprising a glass disk having a surface area larger than that of the through-hole.
This prior art chip-less display panel has the following defects.
(1) For exhausting air, the through hole must be bored either on an anode substrate or on a plate of the hermetically sealed envelope arranged opposite thereto. When the hole is bored on a glass plate of either the anode substrate or the opposite plate, an oil of high viscosity is used in order to prevent cracks and/or notches of the glass plate. Since the oil will stain the glass plate, a strong detergent is used to cleanse it. All these extra steps make the manufacturing process more complicated, and increase the manufacturing costs. Moreover, the super hard drill used in the manufacturing process is easily worn and further increases costs. PA0 (2) The peripheral portion of the hole bored in the glass plate is prone to cracks, even if precautions are taken for working conditions. When the plate is heated to hermetically seal the envelope, cracks often occur and debris may adhere to the display segments made of a fluorescent material layer, thereby impairing the luminance thereof. As a result black spots will appear on the display and may result in defective indication by the display. PA0 (3) Where a cover plate, comprising a flat glass disk is used to seal the hole, the cover plate protrudes from the sealed envelope.